Well, we are not completely sure what kind of wetsuits explanation do you want, but since people are mostly interested in the meaning of 6/5/4 well explain that. 6/5/4 gives us the thickness of the neoprene from which the wetsuit is made (in millimeters). A 6/5/4 wetsuit is made out of 6 mm, 5 mm and 4 mm thick neoprene sheets.
Why different thickness?
Thick wetsuit is much less flexible than a thinner one so wetsuit manufacturers use thinner neoprene on places where you need more flexibility (shoulders, arms, armpits, crotch) and thicker neoprene where you need less flexibility (body, legs).
When to wear a 6/5/4?
There are many factors that influence the feeling of cold so if you want a full explanation check out our wetsuit thickness and water temperature guide and chart. In short? A 6/5/4 wetsuit is used in some pretty freezing waters. This is the thickest wetsuit that is still regularly used for surfing. So use it when the water temperature drops below 48F (9C) and you also have very low air temperatures and wind. Basically U would use this wetsuit if you would be surfing during snowfall! When surfing in that kind of conditions also make sure you are wearing thick wetsuit booties, thick wetsuit gloves and a thick hoodie.